The Forman gradient: a discrete tool for topology-based data analysis

Morse theory studies the relationships between the topology of a shape and the critical points of a real-valued smooth function defined on it. It has been recognized as an important tool for shape analysis and understanding in several applications, including physics, chemistry, medicine, and geography. Morse theory is defined for smooth functions, but recently a discrete counterpart, called Discrete Morse Theory (DMT), has been proposed in an entirely combinatorial setting. DMT introduces the idea of discrete Morse functions as functions that assign values to all the cells of a complex. Based on a discrete Morse function we can impose a partial pairing on such cells and eventually build a combinatorial gradient, also called Forman gradient. The Forman gradient is a very powerful tool as it provides a compact way to represent data without altering its homology. This talk will cover our contribution in developing computational tools, based on the Forman gradient, for the analysis of 2D and 3D scalar fields. I will describe in detail our compact representation for the Forman gradient defined on simplicial complexes and how it can be adapted to the n-dimensional case. Moreover, I will describe our recent work on multivariate data (i.e., collections of scalar fields), and how we can adapt the Forman gradient for analyzing such data in a computationally efficient way.